In the drilling and completion industry, the formation of boreholes for the purpose of production or injection of fluids is common. The boreholes are used for exploration or extraction of natural resources such as hydrocarbons, oil, gas, water, and CO2 sequestration. For enhancing production and increasing extraction rates from a subterranean borehole, the formation walls of the borehole may be fractured using a pressurized slurry, proppant containing fracturing fluid, or other treating fluids. The fractures in the formation wall may be held open with the particulates once the injection of fracturing fluids has ceased.
A conventional fracturing system passes pressurized fracturing fluid through a tubular string that extends downhole through the borehole that traverses the zones to be fractured. The string may include valves that are opened to allow for the fracturing fluid to be directed towards a targeted zone. To remotely open the valves from the surface, a ball is dropped into the string and lands on a ball seat associated with a particular valve to block fluid flow through the string and consequently build up pressure uphole of the ball which forces a sleeve downhole thus opening a port in the wall of the string. When multiple zones are involved, the ball seats are of varying sizes with a downhole most seat being the smallest and an uphole most seat being the largest, such that balls of increasing diameter are sequentially dropped into the string to sequentially open the valves from the downhole end to an uphole end. Thus, the zones of the borehole are fractured in a “bottom-up” approach by starting with fracturing a downhole-most zone and working upwards towards an uphole-most zone.
To avoid the inevitable complications associated with employing differently sized ball seats, the smallest of which may overly restrict the flow through the string, and correspondingly different sized balls, the use of deformable balls and ball seats has been proposed, however the rate at which the balls are forced through the ball seats introduces additional complexities including dealing with different rates of deformation of the selected material since it may not function as desired in downhole environments. Also, despite providing certain advantages over using differently sized balls, the order of fracturing operations is still limited to the “bottom-up” approach.